1. Field of the invention
The present invention relates to a mechanism for heating a substrate, particularly to a mechanism for heating a substrate employed for thin film formation and thin film processing in a thin film-forming process such as CVD or sputtering of a semiconductors.
2. Related Background Art
In formation of a thin film such as of a semiconductor, heating of a substrate is indispensable for obtaining higher quality of the thin film.
FIG. 3 roughly illustrates construction of a sputtering apparatus for film formation having a conventional substrate-heating mechanism.
The film-forming sputtering apparatus 100 as shown in FIG. 3 is of a parallel-plate type, and comprises a vacuum chamber 111 electrically grounded, a target 112 placed in the vacuum chamber, a magnetron electric field-applying means (above the target 112 in FIG. 3) constituted of a permanent magnet 1131 and a yoke 1132, a first earth shield 114 provided around the magnetron electron field-applying means, a DC power source 116 for applying DC voltage through a low-pass filter 115 to the target 112, a high-frequency power source 118 for applying a high-frequency voltage through a matching circuit 117 to the target 112, a substrate holder 119 for holding the substrate 101 such that the film formation face is confronted to the target 112, and a second earth shield 120 provided around the substrate holder 119; and, outside the vacuum chamber 111, a substrate-heating mechanism constituted of a substrate-heating platinum heater 130 placed at the side of the substrate 101 reverse to the film formation face (hereinafter referred to as "back face") and a reflecting plate 131 placed at the side of the heater 130 reverse to the substrate 101.
A gaseous starting material is introduced through a gas introduction valve 121. The vacuum chamber 111 is evacuated through an evacuation opening 122 connected to an evacuation pump (not shown in the drawing). Prior to film formation, the vacuum chamber is evacuated to the ultra-high vacuum range (1.0.times.10.sup.-8 torr or higher vacuum). For this purpose, a metal gasket is employed for sealing the flange portions in the vacuum chamber 111, and Kovar connection is employed for insulating seal. A cooling means is provided at the side of the yoke 1132 reverse to the permanent magnet 1131 to cool the magnetron magnetic field-applying means.
The substrate 101 in the sputtering apparatus 100 is heated at the back side by conduction and radiation of heat generated by the substrate-heating platinum heater 130 through the substrate holder 119.
In the above-described conventional film-forming sputtering apparatus 100, when the film is formed at a high temperature, above 450.degree. C., of the substrate 101, the substrate-heating platinum heater 130 is required to be heat-resistant to such a high temperature to increase the current flow for larger heat generation. However, even with increased capacity of the substrate-heating platinum heater 130, high heating efficiency is not achievable disadvantageously because the substrate 101 is heated from the outside of the vacuum chamber 111 through the vacuum-maintaining portion (namely the substrate holder 119). Further, the increase of the capacity of the substrate-heating platinum heater 130 results not only in higher temperature of the substrate 101 but also in increase of the amount of gas released from the portion of the substrate holder 119 to cause contamination of the film formed on the substrate 101 with impurity.
As one method to solve such problems, the substrate-heating platinum heater 130 is placed in the vacuum chamber 111, thereby eliminating the interposed article such as substrate holder 119 as practiced in MBE (molecular beam epitaxy). With this method, however, the vacuum chamber 111 is heated by thermal radiation from the substrate-heating platinum heater 130, and deposition of a film by diffusion of the gaseous material on the substrate-heating platinum heater 130 causing disadvantages electric breakdown. No report has been presented on a method of decreasing the released gas in the case where the substrate-heating platinum heater 130 is placed in the vacuum chamber 111.
In another method, the substrate is locally heated by direct irradiation of light or the like from the film formation face of the substrate. With this method, film deposition occurs on a portion other than the substrate. When infrared light, near-infrared light, or visible light is used for the heating, high heating efficiency is not achievable because the introduction of light from the film formation side of the substrate will cause film deposition on the lamp itself or light introduction window for projecting light from the outside.